1. Field of the Invention
The present invention relates to a lubrication system of a small vehicle engine wherein a crankcase having an upper case coupled to a cylinder barrel forming a cylinder bore and a lower case separably coupled thereto rotatably supports a crankshaft having an axis in the vehicle width direction, a cylinder head has at one end along the axis of the crankshaft a head side oil passage, and the lower case is provided with a supply source side oil passage communicating with an oil supply source and extended in parallel with the axis of the crankshaft and a branched oil passage guiding oil to the head side oil passage and branched from the supply source side oil passage to be erected upwardly.
2. Description of Background Art
There has been known in JP-A No. 2004-100630 a lubrication system wherein an oil passage communicating an oil filter and an oil cooler disposed on the front surface of a crankcase when an engine is mounted on a motorcycle is provided in a lower case of the crankcase along the axis of a crankshaft, and a branched oil passage branched from the oil passage guides oil to a cylinder head side.
The cylinder head is provided with a head side oil passage positioned at one end along the axis of the crankshaft. In the lubrication system disclosed in JP-A No. 2004-100630, the branched oil passage branched from the oil passage provided in the lower case is connected to the head side oil passage by an oil passage construction arranged in one plane orthogonal to the axis of the crankshaft on one end side along the axis of the crankshaft. To secure a space arranging the branched oil passage, the width of the lower case in the direction along the axis of the crankshaft needs to be set to be relatively large. The degree of freedom in arrangement of the body frame and the exhaust system mounted on a small vehicle is reduced and the bank angle is difficult to secure.